High-Speed 3-D Scanning Particle Image Velocimetry (3-D SPIV) Technique

Abstract

A 3-D Scanning Particle Image Velocimetry (3-D SPIV) technique has been developed to overcome the resolution problem associated with conventional 3-D Particle Tracking Velocimetry (3-D PTV) without requiring the complexity of 3-D holography. The technique employs a high repetition rate Copper Vapor Laser synchronized with a scanning mirror drum and sheet forming optics to scan the volume of interest. 25 or 50 individual mirrors are adjusted to form an array relatively thick laser sheets parallel to each another, hence effectively covering the entire volume of interest (typically 100×100×100 mm³). This device is capable of recording the time evolution of a flow field in 3-D with a temporal resolution of 200 to 400 Hz, which is more than sufficient for most water flows. The digitized 16mm movies are then processed by a combination of techniques: conventional 2-D cross-correlation and 2-D PTV within each plane. Due to the 2D nature of the recorded information, relatively high seeding densities can be used to yield 20,000 to 50,000 vectors per scan, but yet provide the temporal information associated with successive scans at a rapid rate. The physical implementation of this technique, the overview of the processing and some sample images are presented in this paper.